1. Field of the Invention
This invention is related to instruments for determining the distinctness of image of paint films.
2. Description of the Prior Art
Distinctness of image (DOI) is defined as the sharpness of definition of mirror images reflected from the surface of a film. The DOI of a paint film is considered to be of great aesthetic importance, particularly with respect to the overall appearance of automotive finishes.
Measurements of DOI have been by projection of various size image patterns, such as the broken rings known as Landolt rings, onto the painted surface to be evaluated. By assigning a value of 100 to the smallest set of rings and incrementally smaller values to the uniformly increasingly larger rings, a rating scale is obtained. With this method, the image of the reflected rings on the paint film is observed at a specified distance and the film is assigned a DOI value of the number corresponding to the smallest set of rings in which the break is discernible.
This method has the disadvantage of being highly dependent on the visual acuity of the observer and therefore requires an additional step of normalizing the readings of several observers to obtain an accurate value.
For obvious practical reasons, a method of automatically normalizing the observer is needed. This would eliminate the differences among observers and thereby eliminate the additional step required by the conventional method.